1. Field of the Invention
The present invention consists in a circuit switching device for use in a telecommunication network, in particular a public telecommunication network, although the device could find an application in a private telecommunication network. One object of the invention is to provide users with high bit rate digital traffic channels, typically at bit rates in the order of 2 Mbit/s and above, to enable each user to communicate with the others at a high bit rate, on demand, on a call by call basis.
2. Description of the Prior Art
Data transmission systems using modems of the conventional network are conventional in the telephony art. In the current state of the art, such modems offer a maximum bit rate of 56 kbit/s. The required bit rates referred to above therefore cannot be provided with such modems. However, this type of link has the advantage that it can be set up on demand, on a point-to-point and call by call basis.
Another solution to the problem of transporting digital information (possibly digitized speech or images) on demand consists in using digital networks conforming to the ISDN standard, in which each channel offers a bit rate of 64 kbit/s. In this case, users are offered two types of access. A first type of access provides two channels at 64 kbit/s. A second type of access provides 30 channels at 64 kbit/s. The second type offers bit rates approaching the required bit rate. However, the 30 channels are independent of each other. Essentially, this means that there can be different transmission delays from one channel to another. Consequently, even if users choose to divide messages between the 30 channels, they cannot be easily recovered at the receiving end without using reorganization circuits whose complexity is exorbitant given the huge number of permutations of the order of arrival of the 30 channels.
In France, the France Txc3xa9lxc3xa9com network provides high bit rate (e.g. 2 Mbit/s) TRANSFIX lines. The same type of link is used between telephone exchanges or between paris of telephone exchanges. Given the stated object of the invention, these links have the disadvantage that they are not set up on demand, on a call-by-call basis, and must be reserved well in advance. They cannot be changed immediately when the user""s requirements change. These leased lines provide only fixed point-to-point links, in contrast to the previous two possibilities.
A third generation solution uses ADSL (Asymmetric Digital Subscriber Line) techniques. These techniques are mainly used in the Internet. They entail downloading information from data servers to users at a high bit rate, typically in the order of 2 Mbit/s and above. In the uplink direction, which normally carries queries from users to the network, the bit rate is much lower. It is limited to 128 kbit/s, for example. In this case the link is effectively of the call by call type, but is asymmetric in terms of the bit rates offered.
An object of the invention is to remedy the above drawbacks and to propose a solution in which any user can, on demand, obtain access to a channel providing a high bit rate in both directions for communicating with any other user. The basic idea of the invention is to use existing access and information transport equipment. The existing equipment is used to construct a high bit rate telecommunication network and associated switching circuits. The switching circuits provide each public switched network user with high bit rate (typically 2 Mbit/s and above) full duplex symmetrical access. This means that the copper wire pairs connecting a domestic user will continue to be used at least for access at bit rates up to 2 Mbit/s. It also means that the some service possibilities will be retained: charging mode, special services, on demand access.
To solve the above problems, the invention concerns a circuit switching device in which add and drop multiplexer rings organize local distribution of information as soon as possible within the switching hierarchy, at least at lower levels of the hierarchy. If all users were offered a high bit rate link, they would use the high bit rates. Consequently, the number of bits to be processed by the switching network could increase excessively. To avoid the need to manage all of the distributed information in a central unit, switching is organized hierarchically so that only traffic which is not local and which necessitates inter-regional or even inter-continental links is forwarded to distribution centers higher in the hierarchy.
The invention performs the switching in the rings, which therefore provide dynamic circuit switching. To this end the rings are controlled by control signals resulting from real time interpretation of signaling used to set up a call and normally transmitted by a caller.
The invention consists in a circuit switching system in a telecommunication network including an exchange, a set of access units each of which has a primary ring of add and drop primary multiplexers each of which is connected to user equipment units and control means for the primary multiplexers which include means for receiving signaling transmitted by a user equipment unit connected to the access units, and means for producing routing signals corresponding to the signaling, the routing signals constituting control signals for the primary multiplexers of the set of access units for setting up a connection between the subscriber equipment unit and another subscriber equipment unit.